This invention relates in general to spray nozzle assemblies for airless spray guns, or the like, and is more particularly concerned with improvements in the spray nozzle tip, in an effort to substantially reduce or eliminate the build up of residue material in the area surrounding the orifice exit of the spray nozzle tip, in order to enhance the performance and operation of the spray nozzle.
Typically, a spray nozzle is mounted in a spray head of an airless spray gun. It is well known that such spray guns are used to apply liquid products, such as resinous coatings, to a variety of surfaces, including metal surfaces. The liquid product which is applied passes through a specially designed opening or orifice in the spray nozzle tip. The opening is designed so that a specific spray pattern or spray distribution can be applied to the product to be sprayed.
During the operation of the spray gun at pressures of 250 pounds per square inch (PSI) or higher, very fine droplets of the sprayed material will float in atmosphere around the object being sprayed. Due to the high velocity of the spray material exiting the spray nozzle tip, the air containing these droplets is pulled across the spray nozzle tip. The collection of these fluid particles or droplets on the nozzle spray tip and the resultant drying of such droplets on the spray nozzle tip can seriously hamper the performance of the spray nozzle by interferring with the spray pattern or spray distribution having exited the spray nozzle orifice. It is extremely important to keep the spray nozzle tip clean to prevent the build-up of material from affecting the distribution of the spray leaving the nozzle orifice. The improper distribution will result in an improper coating of the object being sprayed.
The problem of collection or build-up of material or particles on the spray nozzle tip is multipled when the product being sprayed is positioned very close to the spray nozzle tip. As the sprayed material bounces off the sprayed object, additional material or particles will permeate the air surrounding the nozzle spray tip resulting in collection of additional material on the tip. Further, increasing the pressure under which the material is sprayed results in a greater velocity of the sprayed material, thereby causing the formation of additional droplets, which are also present in the atmosphere surrounding the tip.
Spray nozzles are generally made of metal, such as carbide, and the surface of any metal object, when magnified sufficiently, exhibits asperities on such surface. The presence of these asperities combined with the very fine droplets in atmosphere surrounding the spray nozzle tip during use, results in the mechanical interlocking of such droplets with such asperities, thereby allowing a collection of material on the spray nozzle tip, which has been heretofore described as being undesirable. As a result of this collection, frequent cleaning and removal of the spray nozzle tip is required to maintain optimum performance.
A specfic example of the use of a spray nozzle and spray gun would be in the lacquering or coating of the inside of cans, prior to filling the can with a food, beverage or like substance. In this application, it is very important to maintain the proper distribution of the spray that is to be applied to the inside of the can. Improper applications of the sprayed material will result in rust or corrosion in the areas inside the cans which are not properly covered with the sprayed material.
An improper coating application can be caused by the collection of the residue of the sprayed material around the orifice of the spray nozzle tip. Such collection or buildup continues until it makes contact with the spray exiting the orifice and thereby adversely alters the spray pattern having exited the spray nozzle.
Furthermore, in the case of lacquering or coating the inside of the can, which process is completely automated, when a nozzle is not spraying the proper distribution or pattern the entire process must be stopped to permit cleaning and/or removal of the spray nozzle. This results in significant downtime of the machine, which condition is also undesirable.
As previously pointed out, the collection of material on the spray nozzle tip also adversely affects the spray pattern having exited the spray nozzle which can result in a sprayed product being rejected as unacceptable, due to an unacceptable or improper spray coating.
Heretofore, attempts have been made to solve these aforementioned problems. As disclosed in my U.S. Pat. No. 4,256,260, there is shown a spray head into which a spray nozzle is mounted, which mounting facilitates the easy cleaning or replacement of the spray nozzle. While this handles pluggage or partial blockage which occurs internally within the nozzle, this solution still requires the shutdown of the entire operation to effect such removal and cleaning.
It would be very desirable to have a spray nozzle, which, because of its own properties, will prevent the adherence and resultant collection of material on the spray nozzle tip, such that frequent cleaning and replacement is not necessary.